It's complicated, typically US rates aren't a flat $/gallon. Most have flat fixed costs (meter fee, availability fees, etc) and then the actual volumetric rate charge is tacked on top of that. In my city the rate is additionally tiered, so the more water you use the more those later gallons cost. Most residential users fall into Tier 1 though, up to 4 CCF (Centicubic Foot or 748 gallons) per month, which is billed at $1.89 per CCF or $0.002526 per gallon.

So it's hard to use the rates alone as there are additionally fixed rate costs (around $10 a month) and other usage is billed differently (commercial and industrial have higher flat rates as well as higher flat volumetric rate). The result is that commercial and industrial users pay higher rates than residential.

Luckily, my city also publishes raw statistics which indicates that, all things averaged together, the water costs around $0.04 per gallon.